Chain adjustment for traveling water screens



June 11, 1963 w. F. HOFMEISTER 3,093,573

CHAIN ADJUSTMENT FOR TRAVELING WATER SCREENS 2 Sheets-Sheet 1 Filed March 25, 1960 June 11, 1963 w. F. HOFMEISTER 3,093,578

CHAIN ADJUSTMENT FOR TRAVELING WATER SCREENS 2 Sheets-Sheet 2 Filed March 23, 1960 FIG. 5.

United States Patent This invention relates to traveling water screens and particularly to the adjustment of the tension of the parallel chains which carry the individual screens or screen baskets in an endless series and which operate over upper and lower sprockets. The sprockets and front guide means for the chain are carried by spaced frame members and the adjustment of chain tension by movement of the upper sprockets is periodically required to compensate for wearing of the chain and for the proper operation of the screen unit.

The screen units are installed in channels used by electric generating stations and other plants for withdrawing large quantities of water from natural watercourses or supplies. The screens prevent debris or large objects from passing through such channels which may be 50 to 100 feet deep because of titles or variations in the water level of the ocean or river. When the front screens facing the flow become clogged, the upper sprockets are turned to drive the chains which lift the clogged screens from the channel for cleaning and the lowermost back screens move under the lower sprockets and to the front of the screen unit. The screens pass between the lower sprockets and a boot-plate with a nominal clearance so that nothing can pass therebetween which would be larger than whatever is allowed to pass through the screens. However, as the chains wear in service, they become longer and allow the screens to contact the boot-plate unless the upper sprockets are periodically raised to take up the increased chain length.

According to the present invention, a certain number of turns of the nuts is always required to raise the screens by the amount of the nominal clearance referred to and by reason thereof, load-sensitive means supporting the nuts threaded on the take-up screws will serve to indicate the disposition of the chains first with respect to the frame and then with respect to the lower sprockets. That is, if the chains are in proper working order and free of obstructions, no indication of a change of loadon the upper sprockets should appear for at least the number of turns referred to. By having, or setting the indicating means at zero-load in effecting said number of turns, the deadweight load of the screens and upper head-shaft and sprockets'is then positively established and the load which thereafter appears is the load which is due to the engagement of the lowermost baskets with the lower sprockets. No significant amount of chain tension is desired and when indicated no further tightening is effected but may be followed by turning the nuts down a given fraction of a turn so that any indicated tension is relieved The principal object of the present invention is to provide readily operable and reliable sensing means for the usual periodical adjustment of the screen chains to the desired minimum tension and without requiring inspection of the screens or chains.

Other objects and advantages of the invention will appear in the following description of the same as illustrated in the accompanying drawings.

In the drawings:

FIGURE -1 is a side elevation of the traveling water screen with the upper housing removed and with the channel and parts of the screen in section;

FIG. 2 is a front view of the traveling water screen Patented June 11, 1963 'ice with the upper housing or hood in place and with parts broken away and sectioned;

FIG. 3 is a horizontal section taken on lines 33 of FIG. 1 showing the front and rear columns of screens and the frame as set in guides in the sides of the channel which is also in section;

FIG. 4 is an enlarged elevation of one take-up means with parts broken away and sectioned and showing the indlicating instrument with part of the other take-up means, an

FIG. 5 is a schematic diagram of the electrical circuits employed for indicating the adjustment of the upper sprockets.

The spaced vertical frame members 1 are joined by cross-braces, not shown, and may comprise a series of separable sections. 'The frame is assembled as it is lowered into the channel 2 with the out-turned flanges 3 of members 1 fitting in the slots of the guides 5 set in the side walls 6 of the channel.

The foot plates 7 at the bottom of the frame are se- The parallel vertical guides 12 at each side of the frame are fixed to the upper ends 13 of frame members- 1 and are spaced for movement of the bearing blocks 14 therebetween. The take-up screws 15a and 1517 are connected to corresponding blocks 14 and extend upwardly between guides 12 and through the bearing plate 16' extending across the upper ends of guides 12.

The upper sprockets 17a and 17b are fixed to the shaft 18 journally supported by bearing blocks 14 and carry the parallel chains 20a and 20b.

Sprockets 17 are driven by the motor 21 through the gear reduction unit 22 driven by the motor and fitted with the drive sprocket 23 carried by the frame platform 24 at the upper end of the screen unit. sprocket 25 fixed on one end of shaft 18 is connected to the drive sprocket 23 by the chain 26 so that operation of motor 21 drives the chains and the screens, generally and hereinafter referred to as baskets, attached to the corresponding links of each chain.

The construction of the basket may be similar to that shown, for example, in Patent Nos. 2,286,332 or 2,428,- 757 wherein each basket comprises an open frame and the screening 27 which is securely attached thereto and across the opening.

Each basket 28 shown in the drawings comprises a frame including transverse and end members. The adjoining transverse members of the adjacent baskets overlap while allowing. relative movement about a horizontal axis which corresponds with the axis of articulation of the corresponding links of the two chains. Each end member of each basket is provided with a bolt for securement to the corresponding link of the respective chains 2i) and includes a flange 31 having a curved outer edge.

Flanges 32 and the guides 33 parallel thereto and fixed to the inside of members 1, provide tracks for the rollers 34 of chains 24) and support the front screens against the pressure of the water flowing through the channel. Baskets 28 including flanges 31 are dimensioned to pass boot plate 10 with a minimum of clearance and to move upwardly from the lower sprockets 11 between the forward, in-turned flanges 32 of members 1 at the front side of the screen.

As the front screens become clogged by debris, the motor 21 is operated to lift the clogged screens up into the upper housing not shown, where the screens are cleaned by high-pressure streams of water. The oper- The large driven ation of motor 21 and the cleaning may be done at regular, predetermined intervals or whenever the difference in water-level ahead of and behind the screens indicate a given condition of clogging of the screens.

The adverse conditions under which chains 20 operate results in wearing of the chain bearings and consequent elongation of the chains until they do not positively engage the lower sprockets 11. Unless the slack is takenup, the chains eventually allow flanges 31 of the baskets to rub the boot plate 10. This is generally to be avoided because of the likelihood of damage to the baskets or wear on the buckets and boot plate, or the misengagement of the chains with the sprockets.

As previously mentioned, the upper sprockets are best adjusted so that the chains positively engage the lower sprockets but without unnecessary tension. Such adjustment is provided for by capstans 37a and 37b which are threaded on take-up screws 15a and 15b and are supported by the thrust bearing units 38a and 38b to lift shaft 18 and the corresponding upper sprockets.

However, to the present time no reliable means for such adjustment has been provided. In the embodiment of the invention shown, the load-sensitive means referred to, comprise the load-cells 40a and 49b assembled on each take-up screw 15a and 15b respectively, to rest on plate 16 and support the thrust bearing units 38a and 381).

Each load cell 40a and 46b is of the construction shown in FIG. 4 wherein the load-cell 4tla includes a sleeve member 41a to which the several strain gauges 42a and 430 are attached and arranged so that a load applied to member 41a increases the electrical conductivity of gauges 42a and increases the electrical resistance of gauges 43a. The gauges are connected to the terminal 44 carried by the protective collar 45 and the leads 46 connect the instrument 47 with both load-cells as shown in FIG. 4.

As shown in FIG. 5, the gauges 42a, 42b, 43a, and 43b of the two load cells are connected to form two separate Wheatstone bridges and each such bridge, as is well known, comprises two input junctions connected to a source of electric current and two output junctions connected to a galvanometer. The gauges are electrically balanced so that the potential between the output junctions is zero and the gauges are differentially arranged so that a load applied to member 41a or 4112 increases the conductivity or resistance of the respective gauges and so that the potential referred to is changed and is indicated by the galvanometer or meters as will be described.

As shown in FIG. 5, the source 55 of direct current and the switch 56 in series therewith are connected to the input junctions 'of the respective bridges. The meters 51a and 51b are provided with the resistors 52a and 52b in series therewith for protection during balancing and are connected to the output junctions of the bridges. The switches 53a and 53b selectively shunt the resistors for regular use of the meters. The ends of the balancing potentiometers 54a and 541) are connected to the input junctions of the respective bridges and the limiting resistors 57a and 57b connect an output junction of each of the bridges with the movable taps of potentiometers 54a and 54b, respectively whereby the bridges may be first balanced by moving the taps referred to until the meters show no output current. After balancing, the capstans 37a and 37b are then alternately turned a fraction of a turn and, accordingly to the said invention, the response of the meters can be interpreted to show whether the chains are free or are being supported in part by the boot plate.

To adjust the chains 20 before wearing of the flanges 31 on the boot plate occurs, the capstans 37a and 37b are turned a predetermined number of degrees or turns to lower take-up screws a and 15b a distance that is known to be greater than the clearance provided between flanges 31 and the boot plate 10. For example, a screen unit having a given screen mesh might have a clearance of of an inch or necessarily less than the screen mesh and such a unit might have take-up screws of a inch pitch. Therefore capstans 37a and 37b would be turned 1 turns and engagement of the flanges 31 with plate 10 would be conclusive. Of course, if wearing of flanges 31 shows that they have been rubbing the boot-plate, there would be no need to turn down the take-up screws. However, the object of the present invention is to provide means for adjustment of the chains before this happens. It should also be noted here, that having lowered the chains by the amount of the clearance, the chains may then be supported in part by the boot-plate and therefore the first step is to determine the same before setting the meters to eliminate the dead-weight load of the chains. This is done by first setting meters 51a and 51b to zero by adjustment of the corresponding potentiometers 54a and 54b. Thereafter, capstans 37a and 37b are turned alternately or simultaneously a fraction of a turn to raise the screws and chains so that in lifting part of the weight of the chains from the boot-plate, an increased load will be indicated by meters 51a and 51b. When a given number of turns of the capstans does not indicate any additional load, the chains are hanging free of or between the boot plate 10 and the lower sprockets. Meters 51a and 5112 may now be reset to zero so that the meters do not show the dead weight load of the chains and screens. The capstans are then turned alternately or simultaneously to raise each take-up screw and the corresponding chains until a load is indicated by the meters. The load referred to indicates the tension due to the engagement of the chains with the lower sprockets. The chains may be considered adjusted to the desired tension or the capstans may be turned back a fraction of a revolution such as a one-third turn to positively eliminate any tension due to sprocket engagement.

A separate load-cell and meter is employed for each chain so that each chain may be adjusted properly despite unequal lengths due to unequal wearing. The invention eliminates unnecessary tension of the chains which reduces the service life of the chains and requires their more frequent replacement.

The indication of the dead-weight load of the chains permits the meters to be set accordingly without regard to the actual magnitude of the loads so that simple and reliable adjustment means may be employed as described. In the screen shown in the drawings, only the forward column of baskets and chains which operate between flanges 32 and guides 33 are supported on boot-plate 10 when the upper sprockets are lowered, as described. In other screens, not shown, vertical tracks may also be provided for the rollers of the chains of the rear column of baskets and in such screens, both columns of baskets would be supported on the boot-plate in the same manner.

Various modes of carrying out the invention are contemplated as being Within the scope of the following claim particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

In a traveling Water screen having a frame, a series of baskets, upper and lower sprockets carried by said frame, a lower boot plate below said lower sprockets and fixed to said frame and cooperating therewith to close the channel in which the screen is installed, chains operating over said sprockets and carrying said baskets, each upper sprocket having and being supported by a take-up screw provided with a capstan supported by the frame and threaded on the screw to raise and lower the sprocket, said chain and baskets having a predetermined clear- :ance between said boot plate and lower sprockets and said frame including guide means for said chains which hold the chains in a column and cooperate with the lower boot plate in the support of the chains on said lower boot plate when the upper sprockets are lowered a distance greater than said clearance, load-sensitive electrical-resistance means mounted over each take-up screw and on the frame and beneath the corresponding capstan to support the latter, and an electrically operative indicator connected to each of said load-sensitive means and responsive to changes in the load carried by the respective load-sensitive means within a given range, said indicator having means adjustable to selectively raise or lower said range so that the dead weight of the chains and baskets on the upper sprockets when the chains are hanging between the lower sprockets and said boot plate is within said range, each indicator in combination with the respective takeup screw and turnable capstan having means to indicate a reduced load when the chains have been lowered and are partially supported within said guide means by said boot plate, and having means to indicate the lifting of the chains from said boot plate to said lower sprockets as when the upper sprockets have been raised the amount of said clearance with no indicated change in load, whereby the upper sprockets are thereupon properly adjusted to provide a minimum positive tensioning of the chains between the sprockets.

References Cited in the file of this patent UNITED STATES PATENTS 1,555,791 Roddy Sept. 29, 1925 2,675,701 Bidwell Apr. 20, 1954 2,867,707 MacDonald Jan. 6, 1959 

